1. Field of the Invention
This invention relates to a luminescent light source and a luminescent light source array, and, more specifically, to a luminescent light source or a luminescent light source array using an LED (light emitting diode) chip. In addition, the invention relates to a lighting system or a liquid crystal display device, etc.
2. Description of the Related Art
A luminescent light source that has a large area and high light use efficiency is disclosed in Patent Document 1. FIG. 1 shows a cross sectional view of a part of such a luminescent light source. In the luminescent light source 11, a white-color or monochromatic light emitting device 13 is arranged in the central part of the back side of a mold unit 14 made of transparent resin, and a reflecting mirror 12 is formed by depositing a metal thin film such as Al or Au, Ag, etc. in a concentric pattern formed on the back side of the mold unit 14. FIG. 2 shows a front elevation in which the light emitting device 13 and the reflecting mirror 22 are represented with the mold unit 14 excluded from the luminescent light source 11. The reflecting mirror is concentric and consists of a plurality of concentrically arranged ring zone shaped reflecting areas 12a, 12b, . . . . 
Thus, at the luminescent light source 11, as shown in FIG. 1, among light exiting from the light emitting device 13, light L1 incident to a central part 15a of the front side of the mold unit 14 (hereinafter referred to as a direct output area) transmits through the direct output area 15a and is outputted to the front side. In addition, light L2 incident to an area other than the direct output area 15a on the front face of the mold unit 14 (hereinafter referred to as total reflection area) 15b is reflected by the reflecting mirror 12 after being totally reflected in the total reflection area 15b, then transmits through the total reflection area 15b, and is outputted to the front face. Thus, in such the luminescent light source 11, expansion A of the light L2 reflected by one reflection area (e.g., 12c) substantially equals to size of the reflection area (e.g., 12c).
In a backlight for color liquid crystal display, use of a multi-color light source such as red LED, green LED, blue LED, etc. allows three primary colors of the color liquid crystal display to exhibit bright color and to offer excellent color reproducibility, than using a white light source such as white LED. However, in the luminescent light source 11 configured as described above, when three light emitting devices of red, green and blue, for instance, are arranged in the central area of the reflecting mirror 12 to configure a white light source, each color will be separated, leading to the problem of irregular color in the luminescent light source 11. In the following we explain the reasons. FIG. 3 represents light behavior of respective colors when the light emitting devices of three luminescent colors 13R, 13G, 13B of three colors, i.e., red, green and blue are arranged in the central area of the luminescent light source 11. For instance, in FIG. 3, red light is represented as LR, green light is represented as LG, and blue light is represented as LB, wherein an irradiated area of red light LR at a certain distance from the luminescent light source 11 is represented as AR, that of green light LG is represented as AG, and that of blue light LB is represented as AB.
In the case of the luminescent light source 11, since positions of the respective light emitting devices 13R, 13G, 13B are slightly offset, output directions of light reflected by the reflection area 12c after being reflected by the total reflection area 15b differ, depending on a color of light, and thus the irradiated areas AR, AG, AB of the respective colors are mutually offset. Accordingly, a region where light of the respective colors overlap to be a white color is a shaded region in FIG. 3. Also as can be seen from FIG. 3, the shaded white light region is narrower than the reflection area 12c, in the outer region of which output light is colored, resulting in irregular light.
To solve such the problem, it is only necessary to subdivide the respective reflection areas 12a, 12b, . . . to design a cross sectional shape of the reflection area according to light of the respective colors. For instance, in a luminescent light source 16 shown in FIG. 4, the reflection area 12c is subdivided into three reflection areas 19a, 19b, 19c, wherein the reflection area 19a is designed so that blue light LB is outputted to the front face direction in the reflection area 19, the reflection area 19b is designed so that green light LG is outputted to the front face direction in the reflection area 19b, and the reflection area 19c is designed so that red light LR is outputted to the front face direction in the reflection area 19c. 
In the luminescent light source 16 thus designed, a region where light of the respective colors overlap to be white light is substantially the same size as the whole reflection areas 19a, 19b, 19c (i.e., the reflection area 12c), as shown in FIG. 4.
As can be seen from the example of FIG. 4, also when the light emitting devices of multiple colors are used, it is learned that if a greater number of divisions of a reflecting mirror of a light source is set, it becomes possible to set in details a traveling direction of light, which thus improves degree of freedom in designing of a light path, enables finer adjustment of the light output direction, and also improves uniformity in optical intensity.
Now, as shown in FIG. 5, on the basis of the reflecting mirror 12 wherein the number of divisions of the reflecting mirror 12 (the number of the reflection areas) is 3, and pitch interval P (width in a radial direction of the reflection area) of the reflection areas 12a, 12b, 12c is 6 mm, consider respective reflection areas that are further divided into three reflection areas. FIG. 6 shows such the reflecting mirror 12. In the reflecting mirror 12 as shown in FIG. 6, the number of divisions of the reflecting mirror 12 is 9, and the pitch interval of the reflection areas 17a, 17b, 17c, 18a, 18b, 18c, 19a, 19b, and 19c is 2 cm. Thus, although use of the reflecting mirror 12 as shown in FIG. 6 could improve color uniformity of a luminescent light source, increased number of divisions will narrow the pitch interval of a reflection area, thus making it difficult to manufacture a reflecting mirror, and increasing cost. In other words, there is the problem that as the number of the divisions of the reflecting mirror 12 increases, a balance between performance improvement and the cost will be lost.
In addition, as the light emitting devices 13R, 13G, 13B are arranged in two dimensions, a distance between the light emitting devices of the respective colors 13R, 13G, 13B and the reflection areas 12a, 12b, . . . differs depending on a direction of viewing. Therefore, in the concentric reflecting mirror 12 in which the respective reflecting areas 12a, 12b, . . . are arranged circumferentially and equidistant around one point, comparable overlap (mixed colors) in the whole circumferential direction cannot be achieved. To describe this concretely with reference to FIG. 4, when the red light emitting device 13R, the green light emitting device 13G, and the blue light emitting device 13B are arranged in this order from the left as one faces, to the left thereof are arranged the reflection area 19a from which red light is vertically outputted, the reflection area 19b from which green light is vertically outputted, and the reflection area 19c from which blue light is vertically outputted in this order from the inner circumference. On the contrary, to the right of the light emitting devices 13R, 13G, 13B, the reflection area 19c from which blue light is vertically outputted, the reflection area 19b from which green light is vertically outputted, and the reflection area 19a from which red light is vertically outputted must be arranged in this order from the inner circumference side. Such the arrangement cannot be implemented with the ring zone shaped reflection areas.